Method for determining optimal placement of electric vehicle chargers

ABSTRACT

A method for the efficient placement of electric vehicle chargers in a target area couples vehicle dynamics and battery dynamics modeling with environmental factors to accurately incorporate the impact that the environment has on the range of the battery into the placement of the chargers by simulating trips of fleets of electric vehicles. The vehicles can be of various types, for example, motorcycles, cars, trucks or aircraft, and will each have their battery state of charge monitored as they traverse a simulated trip through the target area.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/973,541, filed Oct. 9, 2019, the contents ofwhich are incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

The electrification of the transportation industry and growing adoptionof electric vehicles (EVs) has precipitated a concurrent increasingdemand for charging infrastructure. Efficient and optimal deploymentthis infrastructure requires models that can adequately estimate theperformance of the electric vehicle fleet under real scenarios. Whilethere has been significant work on estimating energy-consumption forrealistic drive profiles, there is a need to systematically incorporateenvironmental conditions (e.g. wind, elevation) along a route forenabling efficient and optimal charger deployment.

To efficiently and optimally place chargers, several factors must beconsidered including, for example, the range of the EVs and the cost ofthe infrastructure. Some existing models used to solve this probleminclude a grid-based approach and an agent-based approach.

The grid-based approach places chargers at constant distances from eachother, effectively building a grid of chargers such that any EV is ableto go to a charger wherever and whenever it may be required. While thismethod addresses

the demand consideration for charger placement, it is very expensive asit will deploy far more chargers than are actually needed, resulting insome chargers seeing little to no utilization.

The agent-based approach, on the other hand, places chargers based onthe demand generated using a simulation of several individual agents.This demand is based on a cost function that uses numerous factors, forexample, social influence, fuel cost, etc., which allows this method toplace chargers in a more cost-efficient manner while also meeting thedemand of the EV fleet.

One issue that persists with existing methods is that they treat thebattery as a black box. As a result, the respective models for the EVwill yield a single value for the range rather than a dynamic rangebased on the conditions under which the EV's operate and under which thebattery is utilized.

The range of the EV is dynamic based on the conditions under which thebattery is operating, thus the single range assumption used in theprevious models fails to place chargers in a way that will sufficientlymeet the demand of the EVs under all conditions.

SUMMARY OF THE INVENTION

To address the deficiencies of the existing models, a new method hasbeen developed and is disclosed herein which will utilize the power ofhigh-performance computing to simulate thousands of individual vehiclestraveling through various conditions such as weather and traffic, allwhile calculating the depletion of the battery through the coupling ofboth vehicle and battery dynamics.

This will allow the method to place chargers that will meet the demandof the projected EV fleet under any condition while also minimizing theinvestment cost needed to do so.

The method provides a high-fidelity agent-based electric vehiclesimulation framework which can also simulate fleets of electricvehicles, each recording their own performance, and provide fleetstatistics that can be used to inform larger simulations such as chargerdeployment optimization. The method can simulate any electric vehicle,including but not limited electric cars, electric trucks, and electricaircraft, can use any battery model and can perform this analysis forany location.

In some embodiments, the invention can accurately incorporate the impactthat the environment has on a range of an electric vehicle battery intoa model to determine optimal placement of chargers by coupling vehicledynamics and battery dynamics modeling, thereby properly satisfying thecharging demand of an EV fleet.

In some embodiments, the invention utilizes a map of a target area tocreate a matrix representation upon which simulated vehicles can travel.Such vehicles can be of various types, including, for example,motorcycles, cars, trucks, electric aircraft, electric vertical take-offand landing (eVTOL) aircraft, etc. and each type of vehicle can havetheir own start and end locations generated on a map using eitherstochastic sampling or a biased pick based on known information aboutthe location, for example, whether the location is a shopping mall, workcenter, residential area, etc.

In some embodiments, the invention includes methods that can route eachvehicle through a map from a start location to and end location withhighly accurate energy estimates for the trip. In some embodiments, theState of Charge (SoC) of the vehicle battery can be calculated usingvehicle dynamics equations to calculate the power needed to travel thedistance and then applying battery dynamics equations to calculate theresulting depletion of the battery accounting for environmentalconditions.

In some embodiments, if the SoC of a vehicle gets below a set threshold,a vehicle can travel to the closest charger, otherwise it will continueon its trip. In some embodiments, by using Markov modeling, the tripgeneration for each vehicle can dynamically change, allowing the tripsto include multiple stops across the target map.

In some embodiments, the invention can appropriately place chargers bykeeping track of vehicles and their respective preferred charginglocations. A high-performance computing cluster and parallel programmingmay be used to run several simulations of thousands of vehicles inparallel, with each simulation generating its own heat map for optimalcharger placement.

In some embodiments, by gathering the distributions for each charginglocation for a given input condition set, the convergence of the chargerplacement can be tested. In some embodiments, the invention may includea method to develop the appropriate map data file for each locationbased on measured environmental conditions. For example, the inventionmay utilize Shapefiles measured from a locale along with measured dataof the elevation, wind direction, wind speed and temperature to create amap data file that appropriately captures the dynamics of the targetlocation. In some embodiments, the temporal aspect of the climate canalso be captured by feeding the method the appropriate measured datafrom the respective time of year needed to capture the seasonal effects.Along with the environmental factors, the invention may also factor incharacteristics of the vehicle, such as its drag coefficient, frontalarea, etc., impact the overall energy used to move the vehicle, etc.

In some embodiments, the movement of the vehicle along the route can beaccurately tracked by using representative vehicle drive cycles of thelocal area. The aforementioned factors may allow the invention tocustomize the charger placement to each target location based on itsrespective local conditions. The accurate calculation of the energy usedby the vehicles in a trip can also be extend to areas outside of justcharging such as estimate the real range an electric vehicle will have.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a flowchart showing the overall process to produce arecommendation regarding optimal charger deployment.

FIG. 2 is a flowchart showing the simulation of individual vehiclesexecuting trips within the target area.

FIG. 3 is an example diagram showing hotspots indicating possiblecharger locations.

FIG. 4 shows a map of the state of Massachusetts showing a simulatedtrip used to evaluate individual simulated vehicles.

FIG. 5 is a graph showing the wind speed and elevation profiles alongthe route shown in FIG. 4.

FIG. 6 is a graph showing the power profile for an electric pickup trucktype agent traveling the eastbound on the route shown in FIG. 4, takinginto account the effect of various environmental factors on the powerprofile.

FIG. 7 is a graph showing the power profile for an electric pickup trucktype agent traveling the westbound on the route shown in FIG. 4, takinginto account the effect of various environmental factors on the powerprofile.

FIG. 8 is a graph showing the SoC depletion curves for an electricpickup truck type vehicle for a benchmark trip taking into account noenvironmental factors and for eastbound and westbound trips which dotake into account environmental factors.

FIG. 9 is a graph showing the SoC depletion curves for a Tesla model 3vehicle for benchmark trip taking into account no environmental factorsand for eastbound and westbound trips was to take into accountenvironmental factors.

FIG. 10 is a histogram showing the distribution of distances traveled by1000 simulated agents.

FIG. 11 is a histogram showing the distribution of energy usage per mileof 1000 simulated agents showing bimodal peaks.

FIG. 12 is a graph showing the SoC trends for simulated trips of 1000Tesla model threes showing that, despite random roots picked by eachagent the trends exhibited a bimodal split.

FIG. 13 is a graph showing the SoC trends for simulated trips of 100Tesla model threes were 50 the vehicles had only the elevation effectsand the other 50 had only wind effects, which suggests that the observedbimodal split is due to the wind effect while the spread along each ofthe split is due to the elevation effect.

DETAILED DESCRIPTION

To meticulously simulate individual electric vehicles, and toefficiently and accurately extend the analysis to the fleet level scaleand optimize the fleet level statistics to perform tasks such as chargerplacement, a complex system analysis known as Agent-Based Modeling (ABM)is employed. ABM was chosen for this analysis because of the capabilityto utilize the parallel processing to simulate multiple agents, eachgoverned by a set of mathematical equations and rules and explore thedynamics outside of the reach the reach of just those equations. Eachagent is governed by a set of vehicle dynamics and battery dynamicsequations, each augmented by measured data, such as elevation andtemperature, such that each agent emulates the behavior of an electricvehicle (EV) driving through the simulated area. Each agent from the ABMwill provide information on its performance which will be used todetermine the fleet statistics at the end of the simulation.

In the setup of ABM for this invention, the agents do not interact witheach other. This means that some of more sophisticated dynamics will notbe simulated in this system, such as traffic-based routing, however theagents are therefore individual entities that can be simulated entirelyin parallel. Thus, through the use of parallel computing paradigms, thecomputational cost of the ABM is drastically reduced, allowing for it tobe seamlessly integrated into the optimization schemes using the fleetscale data, such as charger placement. In addition, even simple ABMshave the ability to simulate the complex behavior of real systems andprovide important information about the dynamics that govern thesesystems.

The aforementioned ABM simulation forms the heart of the softwareportion of the invention, which is described in detail herein. The mainadvantage of the invention over other charger placement methods is itsability to consider the battery as a dynamic system while alsoincorporating other factors, including, for example, the impact ofenvironmental factors and conditions to determine the optimal locationfor the chargers. Other prior art algorithms ignore this detail andtreat the electric vehicles as having a fixed range on their respectivebattery packs. This, however, is not the case and has the potential tocause those algorithms to misplace chargers where vehicles are incapableof reaching the chargers before the battery is drained or placing toomany chargers within the target area.

Through the coupled dynamics simulation previously described, theinvention is able to account for the variable range in the battery packof an electric vehicle, including environmental impacts such astemperature, elevation and wind, and place chargers that will properlymeet the demand of the electric vehicle fleet within the target area. Inaddition, the invention is built as a modular algorithm. This means thatit is capable of performing high-fidelity simulations on any electricvehicle, including, but not limited to, electric cars, electricmotorcycles, 3-wheeled vehicles (i.e., tuk-tuks), electric trucks,electric aircraft, etc., and estimating the corresponding fleet dynamicsas well as placing the corresponding chargers/skyports.

Map Generation

With reference to FIG. 1, the first step in the method is map generation102, that converts measured data from the target area into a form whichthe ABM simulation can utilize. This step will have some variationdepending on the mode of transportation that is being evaluated, howeverthe methodologies employed within the algorithm and the end result willbe the same throughout all simulations. Thus, the following descriptionof this step within the method provides both a general overview of itsimplementation as well as some of the particular steps that are taken tosimulate personal electric vehicles such as cars or pickup trucks.

The start of the map generation portion 102 of the method is aconversion of a freely accessible geospatial map data file 10 describingthe target area into a series of RGB matrices indicating the presence ofa road and other data, for example, the expected traffic on the road.The series of map matrices are shown as map matrix 50 in FIG. 1.

In one embodiment, the geospatial file 10 used in this analysis is knownas a shapefile. Shapefiles are the most widely used format for storinginformation, such as road networks, using a variety of vectors,polylines and polygons to describe the encoded feature. In addition,these files will often include different tags or descriptors for each ofthe geometric shapes provided to help identify the object, such as thetype of road that the object is representing. The wide availability ofshapefiles fits well with this method as it allows for any location,regardless of scale, to be simulated, providing that a shapefile whichadequately describes the location exists. The sources for the shapefilescan vary depending on a country-by-country basis, but for locationswithin the United States, shapefiles are obtainable from the UnitedStates Census Bureau.

Once the shapefile is imported, the first step is to scan through thepolylines and determine the maximum and minimum values for both thelatitude and the longitude. These values define the bounding box for thearea of the simulation and thus they will occupy the first and last rowfor the latitude matrix as well as the first and last column for thelongitude matrix created in map generation step 102. This sets thelatitude and longitude matrices up in a mesh grid pattern such that eachelement combination from the two matrices defines the latitude andlongitude coordinates on the map. To determine the grid values inbetween, and ultimately the size of the matrices, the user is asked toinput the desired discretization for both the latitude and longitude inmeters. This user-supplied setting is part of the user-supplied data andsettings shown as 30 in FIG. 1. The following formula is then used toconvert from the desired discretization to the corresponding latitude orlongitude step:

$\begin{matrix}{\delta = {2{\sin^{- 1}\left( \sqrt{\frac{1}{\frac{1}{\tan^{2}\left( \frac{d}{2R} \right)} + 1}} \right)}}} & (1)\end{matrix}$where:δ is the is the step size for either the latitude or the longitude;d is the discretization corresponding to either the latitude or thelongitude that is set by the user; andR is the radius of the Earth in meters.

Once δ is calculated, it is converted from radians to degrees to get theproper step needed for the latitude/longitude. Eq. 1 is derived from thehaversine formulation to calculate the great-circle between two pointson a surface, in this case, the Earth. Note that this formulationassumes a spherical object as well as a smooth surface. As such, thedistance calculated by this formulation will have some error associatedwith it. The formulation is reproduced below:

$\begin{matrix}{a = {{\sin^{2}\left( \frac{\Delta\phi}{2} \right)} + {{\cos\left( \phi_{1} \right)}{\cos\left( \phi_{2} \right)}{\sin^{2}\left( \frac{\Delta\lambda}{2} \right)}}}} & (2) \\{c = {2a\;\tan\; 2\left( {\sqrt{a},\ \sqrt{1 - a}} \right)}} & (3) \\{d = {Rc}} & (4)\end{matrix}$where:ϕ is the latitude;λ is the longitude;R is the radius of the Earth;d is the calculated distance; anda and c are intermediary values which correspond to different geometriclengths within the sphere.

To derive Eq. 1 from Eq. 2-4, the first point is set to 0° latitude and0° longitude. The second point is then set such that the traversal onlyhappens in the direction of interest, such as δ° latitude and 0°longitude if the step for the latitude was being calculated, and dbecomes the user input step size. The step size for the latitude willdetermine how many rows the matrices will have as well as the latitudevalue that will be used in that row while the longitude step size willdetermine how many columns the matrices will have as well as thelongitude value that will be used in that column. In addition, thelatitude and longitude each have their own δ, effectively allowing theuser to control the size of the matrices used for the simulation. Thismeans that the user can set a large discretization for a high level,quick simulation of the area or use a smaller discretization for a moredetailed analysis.

Once the latitude and longitude matrices are constructed, a matrix ofall zeros the same size as these matrices will be made which will formthe basis of the RGB matrix, which is also part of map matrix 50. Thepurpose of the RGB matrix is to encode all of the road information fromthe shapefile as well as the traffic information, if it is available,within a one or more matrices on which the ABM can run the vehiclesimulations. For simplicity, an element of the matrix that has a valueof zero is defined as an empty space on the map, which the agent willnot be able to travel on, while values of one, two or three designatethat the element is a road with traffic levels of green, orange or redrespectively, which will each have different effects on the speed of theelectric vehicle later in the simulation. If there is no trafficinformation input into the script, it will set any road to have a valueof one within the corresponding element of the matrix.

To populate the roads within the RGB matrix, the script takes eachindividual polyline and numerically determines which elements of thematrix fall within that polyline. This is done by taking the first twopoints from the set of points defining the polyline and fitting a linearequation to them in the form of y=ax+b where y is the latitude and x isthe longitude. A check is then performed to determine if the slope iseither greater than 5000 or infinite. If this check is true, a newlinear equation is determined in the form of x=a′y+b′. This is done toensure numerical stability and account for any cases where the linesegment might be vertical, in the case of the infinite slope, as a largeor infinite slope in the first equation means that the second equationwill have a slope that approaches zero. Because the polylines of theshapefiles are a series of linear segments defined by the set points,using the linear fit will ensure that all of the characteristics of thepolyline are captured within the RGB matrix.

The script performing map generation 102 starts at the first point usedto make the linear fit, which is the first point of the polyline,determines which element in the RGB matrix is the closest to that pointand fills in the corresponding value to that element, depending on thetraffic information. Because the latitude and longitude matrices aresetup in a mesh grid format, the closest point in the RGB matrix can befound by finding the argmin of the element-wise square differencebetween one column from the latitude matrix and the latitude value fromthe evaluated point, which gives the row index of the closest point, andthe argmin of the element-wise square difference between one row fromthe longitude matrix and the longitude value from the evaluated point,which gives the column index of the closest point. This can beformalized in the following expression:RGB=[argmin((Y−y)²),argmin((X−x)²)]=t;t∈(1,2,3)  (5)where:x and y are the calculated longitude and latitude;Y is the first column from the latitude matrix; andX is the first row from the longitude matrix.

As stated earlier, the value for t is determined based on the trafficconditions, if provided, that are closest to that point. The script thenenters an adaptive step size routine to determine which elements of thematrix constitute the fitted line. This is done by providing to theroutine the two points which were used to make the line, the fittedequation and the maximum step sizes for both the dependent andindependent variables. These maximum step sizes are defined to be halfof the longitude step used to build the longitude matrix and half of thelatitude step used to build the latitude matrix and which one is usedfor the dependent and independent variables will be dependent on theformation of the linear fit. The routine starts by calculating themidpoint between the two points and, using the fitted equation,determining the corresponding dependent variable. It then checks to seeif the step in the dependent or independent variable exceeds the setthreshold. If the midpoint fails these checks, then the routinerecursively calls itself to split the line segment in half again andexamines the new line segments to see if they pass the checks. Once thechecks are passed, the routine uses Eq. (5) for the points that definethe current line segment that is being checked. This routine allows thealgorithm to dynamically and efficiently determine the points that needto be added to the RGB matrix to fully capture the current part of thepolyline. Once the routine has reached the end, Eq. (5) is used on thesecond point that was used to make the linear fit. The routine thenmoves on to the next part of the polyline by remaking the linear fit andusing the adaptive step size routine using the second and third pointsfrom the polyline set of points. This process continues through theentire set of the polyline points, mapping the geometric shape definedby this polyline into the RGB matrix. Because the processing of onepolyline from the shapefile is completely independent from the otherpolylines, the algorithm for mapping the shapefile into the RGB matrixcan be parallelized over the polylines. This allows for the script to beable to efficiently process large shapefiles that consist of thousandsof polylines within a much shorter time than without thehigh-performance computing.

While the process mentioned above covers conversion of a shapefile intoa matrix for encoding the road information, in alternate embodiments,the method also has the ability to use OpenStreetMaps along with thecorresponding OSM and planetOSM files to create these representations ofthe roads. OpenStreetMap provides a variety of advantages, including,for example, additional framework that can be used to augment roadnetwork information that has been provided through the shapefiles. Assuch, in some embodiments, the OpenStreetMaps may be used in addition tothe shapefiles. As would be realized by one of skill in the art, othersources for map and road data may be used, for example, Google® Maps.

With the shapefile processed into the RGB matrix, the next part of themap generation script can begin to import the relevant environmentaldata 20 which will be used to enhance the dynamics of the agents. Beingable to account for these environmental factors when simulating theelectric vehicles allows the method to effectively and realisticallyestimate the range of the vehicle by taking into account the extra powerload that could be drawn from the battery due to, for example, wind orelevation changes, as well as simulate the impact that temperature hason the dynamics of the battery.

For simulating the electric vehicle, various environmental factors maybe considered, for example, wind speed, wind direction, elevation andtemperature. In some embodiments, the wind and temperature informationmay be obtained using the NREL Wind Toolkit is used for analysisperformed for area within the United States. The NREL Wind Toolkit is a50 TB database of one-hour resolution data which covers the UnitedStates, the Baja Peninsula and parts of the Pacific and Atlantic Oceansover the span of seven years. In addition, the toolkit provides the dataat several different altitudes which is useful for applying the analysisto several different types of vehicles, including, for example, electricaircraft.

In some embodiments, the national elevation map published by the UnitedStates Geological Service (USGS) may be used as a source of elevationdata for the same area covered by the NREL Wind Toolkit. The nationalelevation map comprises the results from many different elevation datasources and has various scales of resolution. To query this database, aseries of points representing the latitude and the longitude must begiven to the system, which will then return the same points with thecorresponding elevation in meters and feet. Thus, the data was firstqueried from the NREL Wind Toolkit for a particular day and then thepoints within this data were broken up into smaller groups of points andautomatically fed into the query system to build an elevation referenceset that uses the same points as the data provided by the NREL WindToolkit. Unlike the NREL Wind Toolkit, which needs to be queried foreach different condition under examination, the process for obtainingthe elevation data only needs to be run once. Any subsequent runs toobtain further elevation data need only be done to update the valuesthat have been queried as the national elevation map is frequentlyupdated.

Once the reference data has been gathered for the environmental factorsof interest, they are interpolated into the map matrices 50. First, theimported data is reconfigured into a set of three matrices wherein thefirst matrix contains the latitude of each point, the second matrixcontains the longitude of each point and the third matrix contains thecorresponding data. A matrix of the same size as the RGB matrix isconstructed for each of the environmental factors and filled entirelywith zeros. The script then visits each element in the RGB matrix anddetermines if it is an empty space or if it contains a road.

If it is an empty space, the script moves on to the next element anddoes not perform the data interpolation as the empty spaces will not berelevant in the calculations that will be subsequently performed. If thespace contains a road, it first uses an expression similar to theleft-hand side of Eq. (5) to determine a point in the referenceenvironmental data that is close to the current element in the RGBmatrix. However, because the reference environmental data is not astructured grid, the point in the reference data found using this methodwill not be the closest point to the element in question of the RGBmatrix. To find the closest point, Eqs. (2)-(4) need to be used. Thisprocess is computationally expensive, however, so the point found usingthe other method will be used as the center of a search window. Thissearch window will encompass approximately 50% of the original referencedata and is also used in the great-circle distance equations. This isdone so that the computationally expensive part of the routine has to gothrough as little data as possible and, thus, the overall process isspeeded up. The routine then uses the distances to determine the pointin the reference data that is closest to the element in the RGB matrix.A 3×3 calculation window, centered on that point, is then extracted andused in an inverse distance weighted, 2D interpolation to determine thevalue of that environmental factor at that element in the RGB matrix.Similar to the polyline discussion above, the calculation of theenvironmental factors for each element in the RGB matrix is independentand can therefore be parallelized to decrease the overall time needed toperform this step.

The map for the ABM simulation is completely generated once the 2Dinterpolation has finished. The result from map generation script is aseries of matrices 50 which will all have the same number of rows andcolumns and will each contain a different set of data of the map. Thesematrices 50 include the mesh grid style latitude and longitude, the RGBmatrix defining where the roads are and, if it was available, thetraffic conditions, and the matrices for each of the environmentalfactors including, but not limited to, the temperature, wind speed, winddirection and elevation. As such, using the same index call on each ofthe matrices will provide the ABM simulation the latitude and longitudeof that element, whether it is a road or not and, and if it is a road,the traffic and environmental conditions at that element.

High-Fidelity Agent Dynamics

The next step in the process is to perform a plurality of individualvehicle simulations 104. To accurately assess the performance of a fleetof electric vehicles, and to more accurately determine the mostefficient and optimal placement of chargers, it may be preferred to runsimulations of vehicles of various types numbering in the hundreds orthousands of iterations. Prior to running the simulations, an additionalmatrix containing existing charger locations and possible future chargerlocations is created and initialized. In addition, several statisticsmatrices are initialized and used to contain data regarding theindividual simulated trips taken by the simulated electric vehicles andoverall fleet statistics. Lastly, individual agents are set up to run aplurality of simulated trips in parallel, depending on the hardwarecapabilities of the platform on which the simulations are being run. Forexample, in a parallel computing environment having 64 cores, one coremay be set aside to manage the execution of concurrent simulations inthe remaining 63 cores. The process may be repeated until the desirednumber of simulations is completed. The total number of simulated tripsmay, in some embodiments, be a user-specified parameter.

A flowchart showing the steps in the simulation of a single simulatedtrip are shown in FIG. 2. At the core of the ABM simulation is thedynamics that dictate the actions of the agent simulating a vehicletraversing the map and the corresponding costs that tie the simulationto the real power usage of the EV. At the beginning of each agentsimulation, the route that the simulated EV will take is determined at202. The first things that are chosen are the origin of the simulatedvehicle and the destination(s) of the simulated vehicle, where thenumber of destinations, in some embodiments, may be a user-settableparameter. In various embodiments, the origin for the simulated vehiclecan either be randomly chosen from all of the elements from the mapmatrices 50 that are roads, chosen an a particular type such as aresidential area, commercial area, etc. or chosen from a supplied listof origins from the user. These options can also be mixed such that someagents are randomly spawned while others are chosen based a suppliedlist or biased to a particular type of area based on a distribution. Forspawning in a particular area, the agent randomly selects a location ofthe selected origin type from a supplied list and then uses thegreat-circle distance equations to determine which element from the mapmatrices is closest to that location and uses that element as theorigin.

In choosing the destinations, the first destination is set by the userto be either random, biased by type or chosen from a supplied list inthe same way that the origin is selected. All subsequent destinationsare then chosen based on a probabilistic transition matrix, set by theuser, which will determine if the agent travels back to its origin orgoes to a separate destination, which can again be chosen using thethree different paradigms previously described. These methods are chosento allow for a wide variety of routes to be simulated in the targetarea, while also providing a way to realistically bias the routes toemulate what might happen during a typical day in that area.

Once the origin and destination(s) are chosen, the method begins bydetermining, at 202, the route that the simulated vehicle will takethrough the map matrix 50. In a preferred embodiment, the routes forthis simulation are determined using a well-known algorithm for pathplanning known as A*, although in other embodiments, any path-planningalgorithm may be used. This algorithm has been widely adopted for itssimplicity in determining the path in a gridded space from an origin toa destination that minimizes the defined cost in a variety of spacessuch as vehicle routing. In addition, this algorithm is highlymodifiable, allowing for additional considerations to be included withinthe determination of the route. For this simulation, in someembodiments, the A* algorithm is set to be allowed to make diagonalmovements within the matrix and the cost is defined to be the distancetraveled as searches through the RGB matrix. In addition, the A*algorithm is restricted to only move on the roads, as would be expectedof a car traveling normally, and can't enter any area in the RGB matrixthat is defined as an empty space (i.e., no roads). This algorithmeffectively allows the agent to determine the route that minimizes thedistance traveled (i.e., the “shortest distance” route) which is acommon method of navigation used by many drivers using navigational GPSunits. This algorithm is first used to find the route between the originand the first destination of the agent and then, if necessary, betweeneach of the subsequent destinations, in the order they were determinedin the previous section of the algorithm. The routes for each pair arethen returned as a series which start at the starting point of the routeand then list each subsequent element in the map matrix that must bevisited, to get to the final destination point in the list.

Because the routes are determined between points in the order that theywere decided, the ending point for the first route, which is the firstchosen destination, will be the starting point for the second route.Thus, one of the points can be removed and the lists merged such thatone large route, comprising of the path taken to get from the origin tothe first and second destinations can be made. This is done for each ofthe determined routes such that the end result of this section is justone large series of points which details the entire path of the agentthrough the map.

With the route of the agent determined, the agent can begin to move thesimulated vehicle through the map and the method tracks the power usageof the agent as well as the resulting depletion of the battery. Themethod starts by setting the initial information of the simulated EV,including, for example, determining the characteristics that describethe EV, such as the coefficient of drag and the frontal area for anelectric car/truck, as well as the initial charge of the battery. Theinitial charge of the battery for the vehicle can be set to either fullor less than full. The initial charge the battery may be sampled from adistribution set by the user such that the battery might only be, forexample, 90% charged or less. This is done to allow the simulation todeal with vehicles that don't go start the route with full charge whichcan happen if, for example, the owner of the vehicle forgot to chargetheir vehicle overnight. The aforementioned characteristics of thevehicle are determined using details provided by the user, which willeither set all of the agents to have the same vehicle characteristics,choose the characteristics from a library of choices or choose thecharacteristics based on provided distributions.

Once everything is initialized, the ABM moves the simulated vehicle tothe next point within the route at 204 and calculates the power neededto move from the previous point to the current one as well as batterydepletion that happened during that movement. This step begins bycalculating, at 206, the distance traveled by the agent in movingbetween those points using the great-circle distance equations. Thealgorithm then determines the power that was utilized by the agent whentraveling this distance. This is done using modified versions of thevehicle dynamics equations that have been implemented in the studies forplatooned electric trucks and eVToLs.

Focusing on an exemplary application of the ground electric vehicles,the key challenge is to determine, at 208, the velocity profile of thevehicle as it travels that distance. This is crucial to accuratelypredicting the power usage in that section of the trip (referred toherein as a “microtrip”). To build the velocity profile for the EV, areference profile is needed that is derived from road types that aresimilar to the ones the agents are traveling on. Velocity profiles are avelocity over time description of the travel of a vehicle when drivingon different roads or through different traffic conditions. Theseprofiles are used in many different ways outside of the scope of thisinvention to measure the fuel economy of a vehicle and are used. Forexample, the profiles may be used to determine if a vehicle meetsregulatory standards. Because the velocity profiles describe forwardtravel along different roads, an assumption is made within the algorithmthat the velocity profile is greater than or equal to zero for all timein the profile. This is necessary because the velocity profile needs tobe transformed into a distance profile to link it to the travel that isdone on the map. Thus, by having a velocity profile that is strictlygreater than or equal to zero, the integrated distance profile, which isassumed to start at zero distance traveled for any route, will bemonotonically increasing for all time of the profile. To ensurestability for calculations done on the distance profile, flat sectionsare shrunk to a single point on the distance profile. Once the finaldistance profile is determined, the velocity profile can be easilylinked to the travel done in the route by the agent.

As stated, it is assumed that each route starts at zero distancetraveled on the distance profile which is the first point of thedistance profile. The elevation and the road grade is then calculated byusing the elevation data corresponding the start and end points of themicrotrip. The method takes note of whether the change in elevation ispositive or negative, which will impact the power drawn from the batterydue to the road grade. The change in elevation is then used inconjunction with the distance calculated for the microtrip to determinean adjusted distance traveled using the Pythagorean Theorem. Theintersection of the distance profile and the adjusted distance traveledby the agent in the microtrip is then calculated to determine the timerequired to travel that microtrip. Due to the monotonic nature of thedistance profile as well as the modifications done to the profile, thisintersection calculation will return only a single point. The velocityprofile up to that time is then extracted and sent to the powercalculation as the velocity of the EV as it went through the microtrip.The distance traveled from the microtrip, as well as the intersectiontime, is stored for use in the next section of the route.

With the velocity profile for this section of the route determined, therest of the variables for the power calculation need to be determined.First, the acceleration for all times in the series are determined using

the following equation:

$\begin{matrix}{a_{i} = \frac{V_{i} - V_{i - 1}}{t_{i} - t_{i - 1}}} & (6)\end{matrix}$where:i is the current element in the series;V is the velocity from the extracted velocity profile;t is the corresponding time from the velocity profile; anda is the acceleration.

For time t=0, the acceleration is set to be the same as the accelerationin time t=1. For all other microtrips, the first element in the seriesuses the last values from the extracted velocity profile of the previousroute segment. The other part that needs to be calculated is therelative wind velocity to the EV. The wind heading, wind speed andaltitude of the wind are extracted from the start point of themicrotrip. The wind speed is then brought down to one meter using theHellmann altitude formula. The Hellmann altitude formula is a simpleapproximation that translates the wind speed from one altitude toanother based on the difference in altitude and an exponent which variesbased on the environment that the wind is in. This is a relatively roughapproximation however it is valuable for providing useful results inmost environments and is used in many different practices. Because thecoefficient varies based on the environment that the wind is in, theroad type is mapped to the coefficients to allow the wind to vary basedon the location of the simulated vehicle on the map.

Once the wind has been translated to an altitude of one meter, acomparison of the wind heading to the heading of the vehicle is done.The wind heading is defined to be 0° when pointing north, 90° whenpointing east, 180° when pointing south and 270° when pointing west andit is assumed that the wind heading that comes from the reference datais unchanged by the translation of the wind from the reference altitudeto one meter in height. The heading of the vehicle can be determinedusing the great-circle equations. It is important to note that for thiscalculation, the bearing of the simulated vehicle will be determined atthe initial point, and it is assumed that the simulated vehicle followsa straight line along a the great-circle arc to the next point. Whilethis assumption will not hold in general, so long as the discretizationof the map is set to be small, the change in heading will not be toogreat as the vehicle travels the microtrip. The equation for determiningthe heading of the vehicle is as follows:0=a tan 2(sin(Δλ)cos(ϕ₂),cos(ϕ₁)sin(ϕ₂)−sin(ϕ₁)cos(ϕ₂)cos(Δπ))  (7)where:λ is the longitude;ϕ is the latitude;θ is the bearing; andϕ₁,λ₁ are the latitude and longitude of the origin respectively; andϕ₂, λ₂ the latitude and longitude of the destination respectively.

The a tan 2 function is significant as it will return the bearing in theappropriate quadrant however the returned value will need to first betransformed to degrees and then translated so that the values fall inthe range of 0° to 360°. Using Eq. (7), it can be seen that a vehicletraveling north has a bearing of 0° degrees, a vehicle traveling easthas a bearing of 90°, a vehicle traveling south has a bearing of 180°and a vehicle traveling west has a bearing of 270°, which matches theheadings of the wind. This means that the vehicle heading can besubtracted from the wind heading to provide the relative angle the windhas compared to the vehicle. This allows for the wind to be decomposedinto the component that is blowing along the direction of the vehicle aswell as the component that is blowing perpendicular to the vehicle(i.e., the crosswind) in addition to the whether the wind is helping thevehicle move forward or working against it. After the components of thewind are determined, the relative wind speed along the direction of thesimulated vehicle is calculated by adding or subtracting the speed ofthe vehicle to the wind speed based on whether the wind is blowing withthe vehicle or against it.

With all of the parameters for the power equations determined, the powerused by the vehicle to traverse the current segment of the route may bedetermined, at 210, using a vehicle dynamics model 60. Parametersspecific to the vehicle 65, for example, drag coefficient, frontal area,etc., may be incorporated into the equations comprising the vehicledynamics model 60. The power due to wind is calculated along theindependent components first and then combined into a single value usingstandard component analysis. The power due to the elevation will beeither added to or subtracted from the total based on the whether thedifference in the height was positive or negative. The power due torolling resistance and inertia can then be calculated without any needfor adjustment using the vehicle velocity and acceleration vectors. Allof the power components for each segment of the route are later combinedto provide a power profile that describes the power drawn from thebattery for each time instance in the extracted velocity profile.

Efficiencies can then be applied on a per instance basis where theefficiencies reduce the power that flows back into the battery, if thetotal power is negative, or increases the power drawn from the battery,if the total power is positive. Multiple efficiencies can be taken intoaccount in this step including regenerative braking efficiencies, motorefficiencies, etc. The end result of this step is the for the segment ofthe route being added to the power profile 70 of the vehicle, which isdirectly drawn from the battery pack.

With the current segment of the power profile fully computed, thecorresponding depletion of hundred will the battery for the currentsegment of the route is computed at 212, using battery dynamics model 75and any relevant battery parameters 80, and incorporating theenvironmental factors, such as the temperature, stored in map matrices50. The total power demand on the battery is supplied by all the cellsin the battery pack. The power per cell is the total power of thebattery pack normalized by the number of cells in the pack. Each cellexperiences an equal power load. In theory, if the variation betweencells is ignored, simulating a single cell is sufficient, and thesimulation results from the single cell can then be scaled for the fullbattery pack. The state of charge (SoC) depletion of a cell issignificantly affected by the temperature of the cell, which, in turn,is affected by the external or ambient temperature. Hence, simulatingthe cell in different temperatures can provide drastically different SoCdepletion profiles. The effect of temperature on the SoC can besimulated using battery dynamic models 75 of different fidelities, forexample, both Pseudo C2D battery models and Single Particle batterymodels can simulate the effect of temperature, however, the fidelity andaccuracy of the models are vastly different. On the other hand, higherfidelity generally leads to higher computation time and, hence, acareful study of the trade-offs is required to choose the model that isappropriate for a given platform.

Once the battery depletion for the segment has been computed by thebattery dynamics model 75, the method checks, at 214, to see if thetotal battery depletion has reached a tracking threshold set by theuser. If not, the process moves to the next node in the route at 204. Ifthe current SoC is below the tracking threshold, a count for the currentmap node is incremented at 215, indicating that additional chargers maybe needed near that node. The process then checks, at 216, to see if auser-settable cutoff threshold SoC has been reached, indicating that thevehicle should proceed to the nearest charger. This is used to ensurethat if, for example, the vehicle had to go to a charger after thispoint, that it has enough charge within the battery to make it to theassigned charger without needing to actually simulate the route fromwhere the vehicle currently is to the assigned charger. If the vehiclehas not passed the cutoff SoC, the process checks, at 220 to see if theend point of the route has been reached. If not, the vehicle moves tothe next node in the route at 204. If the SoC cutoff threshold has beenreached at 216, a counter for the closest charger location isincremented at 218, indicating that the vehicle has visited thatcharger. In one embodiment, the current SoC may be adjusted to take intoaccount the level (typically 100%) to which the battery would have beencharged at the closest charger location and the simulation allowed tocontinue. In other embodiments, if the simulated vehicle has passed thecutoff threshold at 216, then the algorithm records the parameterprofiles and terminates without completing the route.

The parameter profiles, such as the battery pack power, cell power, SoC,vehicle velocity, etc. are stored in a total output vector at 222, sothat the profile over the entire trip can be plotted. Once the route hasbeen terminated, processing moves to the next stage of the calculation,such as charger placement, if all simulations have been completed.

When the method moves on to the next segment of the route at 204, ittakes the next point in the route list as the destination point and usesthe previous destination point as the origin for the microtripcalculations. When calculating the intersection of the distance profile,the segments will eventually add up such that the total distancetraveled will go beyond the maximum value of the distance profile. Oncethis occurs, the algorithm will loop back to the beginning of thedistance profile and create a stitch, if needed, between the finalvelocity value and the first velocity value of the velocity profileusing the acceleration at the end. Thus, the EV is assumed to follow thesame velocity profile(s) throughout the duration of the trip and willcontinuously loop through it as needed.

Fleet Scale Simulation

When a fleet scale analysis is desired, multiple agents using thepreviously described dynamics can be employed to estimate the statisticsof the fleet at 106. An important result of the formation of the agentsin the previous section is that each agent is completely independent.This is because the agents don't route based on the traffic conditionsor popular routes chosen by other agents. While this is not completelyrepresentative of how EVs would navigate using the smart GPS tools thatare available, it still allows for meaningful results as even smart GPStools cannot avoid certain areas. The independence of the agents meansthat the fleet scale simulation can be completely parallelizable acrossthe agents, vastly reducing the computation time needed to produce thefleet scale results. This also means that many more agents can besimulated using high-performance computing, allowing for the fleet scalestatistics to use more data points in the respective calculations,thereby improving the statistical significance of the results while alsoproviding for more map coverage with the agents.

A variety of fleet scale statistics can be simulated within the targetarea using this approach. Hotspots for low SoC can be determined bytracking each agent on the map once it is below, for example, 50% SoCfor the rest of its route. This is the threshold specified as thetracking threshold at 214 in FIG. 2. An example of hotspots is shown inFIG. 3. The information from each agent can be combined to show if thereis any area on the map where SoC has a tendency to be low. Thisinformation can then be used as a justification for where chargersshould be placed such that they are accessible to the vehicles that needthem. In addition, a set of charger locations could be provided to thefleet scale simulation to determine which of the provided locations seethe highest utilization from the fleet and are thus the locations thatshould be focused on for possible charger installation.

If additional information is provided, such as charger cost, servicingtime, etc., an optimization loop can be run on top of this analysis todetermine the optimal placement for chargers such that the demand of theelectric fleet can been met, while minimizing the economic impact byinstalling only the chargers needed by the fleet in the locations thatwill best service the fleet. At 108, the information regarding theoptimal charger deployment is output.

Results and Discussion

The invention as a platform augments traditional vehicle dynamics modelsusing geospatial wind and terrain data to monitor change in wind andelevation over a route as well as high resolution temperature data whichwill impact the battery dynamics. Each of these aspects affects thepower requirements of terrestrial vehicles to a varying extent. The winddata is used to create wind vector components both in the direction oftravel for the vehicle and perpendicular to the vehicle to determine theadditional power needed to overcome the wind and/or how much the wind isaiding the vehicle in its travel. The elevation data is used todetermine the road grade throughout the route and whether the vehicle istraveling uphill or downhill, which will change the power associatedwith the vehicle traveling on a slope. The temperature impacts theoverall performance of the battery within the vehicle and will impactthe degradation of the battery.

Using the platform of the invention, a variety of simulations can beperformed to obtain high-fidelity data and statistics on both individualvehicles and fleets of electric vehicles.

Individual Electric Vehicle Case Study—To demonstrate the capabilitiesof the invention for the simulation of individual vehicles, a case studywas constructed where the impact of the environment was evaluated over atrip from one end of the Commonwealth of Massachusetts to the other. ATesla Model 3 as well as an electric pickup truck were used to bothbenchmark the performance of the method of the invention relative topreviously validated work as well as to demonstrate the impact of theaforementioned environmental factors on the vehicle dynamics of thesetwo different vehicles.

For this analysis, the roadway network for Massachusetts will be itshighway system, obtained from a shapefile made in 2015 provided by theUSGS. The wind and temperature data were obtained from the NREL WindtoolKit and were recorded on 12/21/15 at 12:00 pm, while the elevation datacomes from the USGS national elevation map. The wind speed was taken at10 meters altitude while the air temperature was taken from 2 metersaltitude, both of which are the closest to the surface heights for thoseparticular attributes offered through the NREL data set. The drive cycleused throughout this analysis, as well as the fleet analysis is the EPAHighway drive profile (HWFET). Because this drive cycle is repeatedmultiple times throughout the routes, the tails of this drive cycle weretrimmed such that the input drive cycle starts and ends at around 30mph.

For this case study, a single route was used within the aforementionedsetup with the environmental impacts added one by one to discern howthey affect the overall power requirements of the vehicles.

The route chosen for this simulation has one endpoint at 42.7214°latitude and −73.265° longitude, while the other endpoint is at 42.0443°latitude and −70.2153° longitude. The route between these two points, ascalculated by the A* algorithm, is shown in FIG. 4 where(42.7214,−73.265) is the coordinate pair of the northwest point and(42.0443,−70.2153) is the coordinate pair of the southeast point. Thisroute is approximately 263 miles long and, using the modified HWFETdrive profile, will take about 5.3 hours to drive. Both of these valuesare similar to those that are produced through the Google® Maps routingfunction, thus the route and drive cycle used for this analysis can bedeemed as a realistic option for vehicles traveling between these twopoints in Massachusetts.

For this analysis, there is no traffic considered between the twopoints. Thus, the aforementioned values needed no modificationsthroughout the simulation. Using the determined route, the method plotsthe profiles of the environmental factors to see how they change as thevehicle travels from one point to the next. Starting from the northwestendpoint, coordinate pair (42.7214,−73.265), and ending at the southeastendpoint, coordinate pair (42.0443,−70.2153), the profiles aredetermined by querying the supplied environmental databases at eachpoint along the route.

The wind speed and elevation profiles are shown in FIG. 5. From theseprofiles, it can be seen that the wind is blowing the strongest, atabout 8 m/s, in the northwestern part of the route, where the elevationis the highest, decreases to a wind speed of about 3 m/s in the middlepart of the route and then slightly increases at the coast. Theelevation is also the highest in the northwestern part of the route andthen decreases towards sea level, zero elevation, as the routeapproaches the coast. These two profiles correspond very well with eachother where the oscillations and characteristics in the wind profileoccur at nearly the same point of the route as in the elevation profile.This makes sense as wind tends to blow more strongly at higherelevations. This tends to validate the reliability of the different datasets as these two data sets do not interact with each other within theframework of the method and thus have no knowledge about the trendsexhibited by one another.

The temperature and the direction that the wind are blowing remainrelatively constant throughout the entire route, with a temperature ofabout 280° Kelvin and a wind heading of about 120°, which means that thewind is predominately blowing from west to east.

An in-depth analysis of the impacts of the different environmentalfactors within this route was performed using the method for both anelectric pickup truck as well as a Tesla Model 3. For the Tesla Model 3,the drag coefficient of the vehicle was set to 0.23 with a frontal areaof 2.22 m² and a coefficient of rolling resistance of 0.0071. The massof the vehicle was set to 1800 kg while the regenerative brakingefficiency is set to 80% and the battery-to-wheels efficiency, whichincludes the efficiencies of the drive train and the battery, is set to85.5%. For the electric pickup truck, the coefficient of drag for thepickup truck was 0.4 with a frontal area of 5.5 m² and a coefficient ofrolling resistance of 0.0075. The mass of the vehicle was set to 3000 kgwhile the regenerative braking efficiency was 40% with abattery-to-wheel efficiency of 76%. For these simulations, the minimumSoC threshold was set to 30% and the agent, which was set to have theelectric pickup truck characteristics for the results discussed below,was assumed to start with a battery SoC of 100%. The battery model usedto estimate the SoC from the power profile is the CelLFit model wherethe power profile generated from the vehicle dynamics model is scaled toa single cell by assuming that the battery packs in both vehicles have8,000 cells each.

The first set of simulations had the agent start at the northwestendpoint of the route and travel as far as it could towards thesoutheast endpoint. The first simulation has both the elevation and windturned off, which is essentially the benchmark case that was previouslydiscussed. The next simulation kept the wind turned off but beganapplying the change in elevation impacts to the power requirements ofthe simulated vehicle. The following simulation added in the windeffects while keeping the elevation effects turned off. The lastsimulation looked at the total impact of both the elevation and the windon the performance of the vehicle. The power profiles for each of thesesimulations is shown in FIG. 6. Using the power profiles as well as thetotal distance traveled, the average energy used per mile can becomputed for each of the simulations. As previously mentioned, theaverage energy used per mile for the no environment factors case was570.75 Wh/mi and traveled 118.5 mi before hitting the SoC threshold.When evaluating the other simulated scenarios, the average energy usedper mile in the case with only elevation considered was 630.64 Wh/mi andtraveled 106.9 miles before hitting the SoC threshold, the averageenergy used per mile in the case with only wind considered was 447.34Wh/mi and traveled 152.2 miles before hitting the SoC threshold and theaverage energy used per mile in the case with both the wind andelevation effects was 495.39 Wh/mi and traveled 136.6 miles beforehitting the SoC threshold.

When comparing just the elevation impacts to the base case with noenvironmental impacts, the vehicle required about 60 Wh more per mileand, as a result, traveled about 12 miles less before hitting the SoCthreshold. This is because the northwestern area of the route, as isshown in FIG. 5, has a lot of large elevation changes and thus thevehicle needs to expend more energy from the battery to get up thosehills. While it does recover some of that when going downhill, the factthat the regenerative braking efficiency isn't 100% and the vehiclewinds up going back up hill throughout this part of the route means thatthe overall change in the energy requirement per mile will go up. Inaddition, the vehicle in this case is unable to reach the section of theroute where it is primarily downhill and thus doesn't get the downhillbenefit which would have reduced the overall energy required per mile.

The wind only case, on the other hand, uses about 123 Wh/mi less and istherefore able to travel nearly 34 miles beyond where the base casefinished before hitting the SoC threshold. This is because the wind ispredominately blowing from west to east, which practically matches theheading of the vehicle as it travels along the route starting from thenorthwest endpoint. Thus, as the vehicle travels, the wind helps push italong and reduces the overall energy requirement of the vehicle totravel that distance.

In the simulation that incorporates all of the environmental factors,the vehicle is able to travel an additional 18 miles relative to thebase case since the vehicle requires about 75 Wh of energy less per miletraveled. In this case, the vehicle is able to benefit from the windjust like in the previous case, however, now it will start to feel thepenalty of having to power its way up the hills within that area. Thus,as expected, while the energy usage per mile for this vehicle is largerthan the wind only case however, the penalty from the elevation is notas severe since the wind is able to help the vehicle reach the part ofthe elevation profile where it is essentially just moving downhill.Thus, during that portion of the trip, the vehicle receives energybenefits from both the wind and the downhill road grade. When all of theenvironmental factors are considered, the electric pickup truck iscapable of traveling about 15% farther relative to the base case. Thisvariability, relative to what is expected from just looking at themanufacturer characteristics of the vehicle, has a variety ofimplications on what the vehicle operators should expect as well as onthe development of the infrastructure needed to support these vehicles.

To further show the importance of considering these environmentalfactors, the following simulations used the same route, environmentalconditions, vehicle characteristics and approach except that now theystart at the southeast endpoint of the route and travel towards thenorthwest endpoint of the route.

The power profiles for the vehicle traveling the route under theseconditions in the different scenarios is shown in FIG. 7. Because thebase case has no environmental factors considered, the energy usage permile, as well as the total distance traveled, are the same as theprevious simulations. The reason for this is that the route without anyenvironmental factors is essentially the same as a long, straightrunway. Without any external factors, the vehicle will travel the samedistance along the runway regardless of whether it starts on one end ofthat runway or the other end. For the simulation that only had theelevation considered, the vehicle used 578.31 Wh/mi and was able totravel 117.3 miles before hitting the SoC threshold, while in the casethat considered only the wind, the vehicle required 641.74 Wh/mi and wasable to travel 105.4 miles before hitting the SoC threshold. In the casethat considered both the wind and the elevation, the vehicle required643.03 Wh/mi and was able to travel 105.3 miles before hitting the SoCthreshold.

In the case where only the elevation was considered, the vehicle onlyrequired 8 Wh/mi more than the base case and thus traveled only about 1mile less than the base case. This is because, as shown in FIG. 5, thechange in elevation in the southeastern portion of the route is fairlyminimal. In addition, the vehicle hits the SoC threshold just as itenters the part of the route where it begins to have significant uphillgradients. Thus, the vehicle doesn't require that much more energy permile than the base case where no environmental factors are considered.

The wind only case, however, required about 70 Wh/mi more than the basecase resulting in the vehicle traveling approximately 13 miles less thanthe vehicle in the base case. This is due to the fact that, unlike whenthe vehicle travels west to east, the vehicle in this case is travelingagainst the wind. Therefore, the vehicle will require more energy totravel in that direction, resulting higher energy used per mile and lessdistance traveled.

The case where all of the environmental factors are considered isessentially the same as the wind only case due to the fact that theenergy penalty due to the wind results in the vehicle hitting the SoCthreshold before reaching the part of the route with the significantuphill gradients.

These simulations highlight the importance of accounting for theenvironmental factors when considering the performance of the electricvehicles for infrastructure development and driving/pilotingexpectations.

Unlike for the eastbound simulation, where all of the environmentalfactors were considered and where the vehicle was able to travel about15% further than the base case, the vehicle with all of theenvironmental factors considered for the westbound simulation traveledapproximately 11% less than the base case. Thus, if, for example,charging stations were deployed using the black box estimates for therange of the vehicle, which would essentially be equivalent to the basecase scenario in this simulation, there is a chance that the vehiclestravelling westbound on this route might not make it to the chargingstations before running out of charge in the battery. In addition,because these environmental factors are dynamic, the estimation for theoperational range of a vehicle will vary throughout the year even in asingle location. Thus, in depth studies are needed for the differentlocations, including their environmental patterns, to properly place theinfrastructure for electric vehicles to ensure that the terrestrialvehicles can make it to a charger as easily as gasoline vehicles canreach a gas station if needed and that electric aircraft are capable ofmaking it from one station to the next without running out of powermidair.

Observing the SoC trends for the entire route further demonstrates theimpact that the different environmental factors have on the vehicles.The SoC trends for the vehicle traveling with no environmental factors(the benchmark), for the vehicle traveling from the northwest endpointto the southeast endpoint of the route with all of the environmentalimpacts, referred to as eastbound, and for the vehicle traveling fromthe southeast endpoint to the northwest endpoint of the route with allof the environmental impacts, referred to as westbound, are shown inFIG. 8.

The first approximately 50 miles of the route shows all three of thedifferent scenarios behaving fairly similarly, with the westboundscenario having the highest SoC. This is due to the fact that in theeastbound case, the large uphill gradients experienced by the vehiclerequire more energy and, while the wind is offsetting some of it, thewestbound case only has to deal with the wind against the vehicle. Inaddition, as seen in FIG. 4, the first part of the westbound routeactually has the vehicle traveling with an eastern/southeastern heading,thus it will receive benefits for traveling with the wind. However, oncethe eastbound case makes it past the larger elevation gradients, thepower requirement needed to overcome elevation changes decreases as thewind continues to push the vehicle while the vehicle traveling westboundstarts to travel against the wind. Thus, the eastbound case starts tohave a larger SoC than the westbound case.

By the time all of the vehicles have reached the SoC threshold, theeastbound case was able to travel over 30 miles further than thewestbound case, which is nearly an additional 30% in distance traveledrelative to the westbound case, due solely to the different impacts theenvironmental conditions had on the two vehicles. The case of theeastbound vehicle has one other interesting feature in that the SoCstays at 100% beyond the start of the simulation. This is because thevehicle starts at a high elevation and is moving both with the wind anddownhill. As a result, the vehicle has a net influx of power to thevehicle and, while the battery isn't being charged (because it's alreadyat 100% charge), the vehicle is able to travel the first few miles ofthe route without depleting the battery.

The same analysis presented above was also done for vehicles that usedthe Tesla Model 3 characteristics. The SoC trends for the vehicletraveling with no environmental factors, (the benchmark), for thevehicle traveling from the northwest endpoint to the southeast endpointof the route with all of the environmental impacts, referred to aseastbound, and for the vehicle traveling from the southeast endpoint tothe northwest endpoint of the route with all of the environmentalimpacts, referred to as westbound, using the Tesla Model 3 vehiclecharacteristics are shown in FIG. 9. Unlike the vehicles, which used theelectric pickup truck characteristics, the vehicles which used the TeslaModel 3 characteristics are able to travel a majority of the route andcan further show how the environmental factors can compound to causelarger energy penalties/benefits for the vehicle. The trends for the SoCusing the Tesla Model 3 curves have similar features to the SoC trendsshown for the electric pickup truck. However, the curves for the TeslaModel 3 are much tighter together. This is because the coefficient ofdrag for the Tesla Model 3 is significantly less than that for theelectric pickup truck. Thus, the benefit/penalty for travelingwith/against the wind is not as drastic, even though it still does havea dominant effect as will be shown later. In the case of the eastboundvehicle, the wind helps the vehicle with overcoming the elevationchanges, thus balancing the penalty due to uphill elevation changes, butit isn't until the second part of the route where the vehicle isessentially only traveling downhill and with the wind that the vehicleovertakes the other two cases with respect to the SoC. By the end of theroute, the vehicle has an SoC of 46.8% which is only marginally betterthan the base case, which was able to complete the route with an SoC of45.3%.

The westbound case, however, shows how taxing it is for the vehicle tobe traveling both uphill and against the wind, even with a vehicle thatis relatively aerodynamic. In the early parts of the route, where thevehicle is essentially just traveling against the wind, the curve dipsbelow the benchmark but isn't overly taxed by the wind and would havefinished the route, if it kept the same trend, with an SoC marginallyless than that of the benchmark case. However, once the vehicle startsto travel uphill, the SoC gradient drastically increases and the SoCstarts falling much faster than the other two cases. As a result, thevehicle in this case is unable to finish the route before hitting theSoC threshold with approximately 5 miles left to travel. While thedistance traveled is only a 5 mile difference between the eastbound caseand the westbound case, the fact that the eastbound case still had 46.8%SoC meant that it could, if it followed the same SoC depletion trend,have traveled approximately 80 additional miles beyond where it stopped.Thus, even for passenger vehicles, it is necessary to account for theenvironmental impacts as they will alter the expected ranges of electricvehicles.

Vehicle Fleet Case Study—To showcase the capabilities of the method ofthe invention to analyze fleets of vehicles, a case study was performedon 1000 Tesla Model 3s. These vehicles carry the same assumptions andcharacteristics as detailed in the previous section, however, in thiscase, rather than traveling on a fixed route, each vehicle is allowed torandomly pick both a starting point and an ending point and will travelthe route determined by the A* algorithm between those two points. FIG.10 shows the distribution in the distances traveled by the agents. Asshown in the FIG. 10, a majority of the routes picked by the agents areless than 100 miles with an average route distance of 73.3 miles,although there are some agents that travelled large distances with themaximum route distance being 226.2 miles. As each agent traveled theirrespective route, they kept track of information such as the SoCdepletion of the vehicle. The SoC trends of all of the agents is shownin FIG. 12. As seen in FIG. 12, there is a bimodal split in the SoCtrends of the agents. When looking at the vehicles which have traveledmore than 200 miles, there was a vehicle ending its route with 64.6% SoCafter traveling 206.2 miles, which followed the SoC trend of the uppergroup. Another vehicle, however, ended its route with 38.4% SoC aftertraveling 212.7 miles, which followed the SoC trend of the lower group.Thus, two vehicles that had routes with over 200 miles to cover anddiffered in distance by only 6.5 miles ended their routes with adifference in their SoC of their respective batteries, of 26.2%, adifference which was almost entirely caused by differences in theenvironmental effects each vehicle experienced.

Despite the fact that the agents were allowed to randomly chose theirroute, effectively allowing them to span the entirety of theMassachusetts highway system, the SoC depletion of any particular agentis likely to fall into one of these two possible groups, especially forlarger routes. The question that remains, however, is what is the effectthat caused the bi modal split? To answer this, a smaller fleet of 100vehicles was simulated. However, for this simulation, 50 of the vehiclesonly had the elevation changes impact their power profile while theother 50 vehicles only had the wind impact their power profile. The SoCdepletion curves for this simulation are shown in FIG. 13. As seen inthe figure, the vehicles that only had elevation changes impact theirpower profiles tended to stay along one trajectory. However, thestandard deviation of where the SoC is in that trajectory is muchlarger. On the other hand, the vehicles that only had the wind impacttheir power profiles had the bimodal split that was previously observedand the SoC profiles that followed those trajectories had a very tightstandard deviation on the SoC at a given route time. Thus, it can beconcluded that the bimodal split observed in FIG. 12 is due to thedirection the vehicle is traveling, either with the wind or against it,while the standard deviation of the SoC along those two separatetrajectories is due to the different elevation changes the vehiclesexperienced in their respective routes. It is important to note,however, that routes do exist which are traveling orthogonal or nearlyorthogonal to the wind and thus lie in between the apparent bimodalsplit. These routes, due to the shape of Massachusetts, are much smallerand will end before the larger routes, which must be formed from somesection of road which is predominately traveling either with the wind oragainst it, because the wind in this case is predominately blowing fromwest to east. Those shorter routes which could be travelingpredominately northward or southward are what fill in the gap betweenthe bimodal split for route times less than 8,000 seconds.

Therefore, the bimodal split is caused not only by the wind but also bythe geometric constraints of the area. The wind effects are responsiblefor creating the two extremes, while the geometric constraints of theroads are responsible for the lack of SoC curves in between the twoextremes beyond 8,000 seconds. This kind of simulation not only showsthe capability for the method to keep track of the dynamics of multipleagents at once, but also demonstrates the large spread in SoC depletiontrends due to the incorporation of environmental impacts into thevehicle and battery dynamics models which would, if using a black boxcalculation, be completely masked by a single SoC trend.

Using the power profiles corresponding to each of those SoC trends, theenergy used per mile traveled for each of the agents can be determined.The histogram for the Wh/mi of each of the agents is shown in FIG. 11,which shows that the energy usage per mile follows the same bimodalsplit that was previously discussed with respect to the SoC trend.Fitting a Gaussian Mixture model to the data with two distinct means tomatch the bimodal aspect of the data shows that the first peak occurs at183.79 Wh/mi while the second peak occurs at 243.58 Wh/mi. Thus, TeslaModel 3s that travel with the wind, in this case, use on average about60 Wh less per mile traveled. For a Tesla Model 3, this is a significantchange in the energy usage per mile and could have major implications onthe vehicle's ability to reach a charging station, if, for example, thecharging stations are not deployed with these environmental impactstaken into consideration.

CONCLUSIONS

The method of the present invention combines Agent-Based Modeling withwell-calibrated and tested vehicle and battery dynamics models whileincorporating environmental and local effects to properly simulateelectric vehicles and estimate their performance based on specificscenarios At an individual scale, the simulations demonstratesignificant impacts that environmental conditions have on vehicles,causing, in this case, a differential of up to 30% in range traveled.The scale of the analysis can then be easily expanded to fleets ofvehicles to provide statistics on the performance of the fleet which, inthis case, has shown that the environmental effects combined withgeometric restrictions due to the geography of the road network has ledto a bimodality in the energy used per mile for the vehicles. Thisanalysis has shown the importance of including the environment in theestimation of the performance of individual vehicles, which has furtherimplications on the performance of the fleet and deployment ofinfrastructure needed to support that fleet. The method provides theability to perform this in-depth analysis at both the individual vehicleand fleet scale and provides the crucial information needed to properlyanalyze the fleet and make decisions such as where to place the chargingstations. Furthermore, the method is capable of providing this analysisfor any location using freely available data and can seamlesslyintegrate into many different large simulations needing eitherindividual vehicle or fleet scale data, while also being able toincorporate the many different models needed to simulate the differenttypes of vehicles and batteries.

The invention has been described in terms of specific implementations.As would be realized by one of skill in the art, the various specificand limitations are provided as exemplary implementations, modificationsof which are still intended to be within the scope of the invention. Forexample, sources of data used in the simulations, such as map data,environmental data, etc., may be obtained in any form from any source.Likewise, the map of the target area is not limited to storage in aplurality of matrices but may be stored in any convenient way. Specificmethods of formatting and converting the data for use in the simulationsshould be considered exemplary in nature and variations are still withinthe scope of the invention. Similarly, the method of performing thevehicle simulations should be considered exemplary in nature, variationsof which are also intended to be within the scope of the invention.

The invention claimed is:
 1. A method comprising: generating a map of atarget area, the map comprising one or more nodes, each nodecorresponding to a geographic portion of the target area, each nodecontaining one or more characteristics of the portion of the target areato which it corresponds; simulating a plurality of trips of a pluralityof simulated electric vehicles through the target area, each of theplurality of electric vehicles having a battery, each simulationcomprising: determining a route for the simulated trip, the routecomprising a series of nodes from the map; for each current node in theroute: determining a power profile required for the vehicle to move froma previous node to the current node; determining depletion of thebattery from the previous node to the current node based on thedetermined power profile; determining if a state of charge of thebattery falls below a predetermined threshold and, if so, determiningthe nearest node comprising a charger location; ending the simulationwhen the state of charge falls below the predetermined threshold or whenthe vehicle reaches an end node in the route.
 2. The method of claim 1wherein the map comprises one or more matrices, each cell in each matrixcorresponding to a node in the map, each cell in each matrix containingdata representing at least one of the one or more characteristics. 3.The method of claim 1 wherein nodes in the target area which do notcontain or are not part of a road are ignored for purposes of theplurality of simulated trips.
 4. The method of claim 1 wherein the powerprofile required for the vehicle to move from the previous node to thecurrent node is extracted from a power profile for the entire trip. 5.The method of claim 1 further comprising: determining a distancetravelled as the vehicle moves from the previous node in the route tothe current node in the route; determining a velocity profile of thevehicle as it moves from the previous node to the current node;determining the power profile required for the vehicle to move from theprevious node to the current node, the power profile based on thedistance travelled and the velocity profile.
 6. The method of claim 5wherein the velocity profile required for the vehicle to move from theprevious node to the current mode is extracted from a velocity profilefor the entire trip.
 7. The method of claim 1 wherein the one or morecharacteristics of each node comprise the location of the node andenvironmental conditions at the node.
 8. The method of claim 5 whereinthe one or more characteristics of each node comprise trafficinformation and further wherein the velocity profile of the vehicle asit moves from the previous node to the current node is dependent uponthe traffic information.
 9. The method of claim 7, wherein theenvironmental conditions comprise wind speed, wind direction, elevationand temperature.
 10. The method of claim 1 wherein the route comprises astart node and an end node.
 11. The method of claim 10 wherein the startnode and the end node are selected at random or based on the sampling ofthe distribution.
 12. The method of claim 11 wherein the route isdetermined using a routing algorithm.
 13. The method of claim 1 whereinthe power profile is determined by a vehicle dynamics model.
 14. Themethod of claim 13 wherein the vehicle dynamics model is specific to avehicle type and is customized by parameters specifying characteristicsof a particular vehicle.
 15. The method of claim 14 wherein theparameters specifying characteristics of the particular vehicle areuser-supplied values or are sampled from a distribution.
 16. The methodof claim 9 further comprising: determining a positive or negative windcomponent in the direction of travel of the vehicle based on the windspeed and the wind direction stored for the current node in the route;and adjusting the power profile required for the vehicle to move fromthe previous node to the current node based on the wind component. 17.The method of claim 9 further comprising: determining a positive ornegative elevation change from the previous node in the route to thecurrent node in the route; and adjusting the power profile required forthe vehicle to move from the previous node to the current node based onthe elevation change.
 18. The method of claim 9 wherein the depletion ofthe battery is determined by a battery dynamics model.
 19. The method ofclaim 18 wherein the depletion of the battery for the current node isdetermined as a function of the temperature at the current node.
 20. Themethod of claim 1, wherein the resolution of the nodes is set by auser-supplied variable.
 21. The method of claim 7, wherein the one ormore characteristics of each node further comprises whether the node isa charger location.
 22. The method of claim 21 wherein the node is acharger location if the node currently contains one or more electricchargers or is identified as a possible location for one or moreelectric chargers.
 23. The method of claim 21 further comprising:determining the total number of trips from the plurality of simulatedtrips for which each node identified as a charger location was a closestnode to the vehicle when the state of charge of the battery of thevehicle dropped below the threshold.
 24. The method of claim 23 furthercomprising: determining a predetermined number of nodes having thehighest total number of trips; and identifying the predetermined numberof nodes as possible locations for charger deployment.
 25. The method ofclaim 1 wherein the initial state of charge of the battery for eachsimulated trip is set to a random value.
 26. The method of claim 1wherein the initial state of charge of the battery for each simulatedtrip is set by sampling a distribution.
 27. The method of claim 1wherein a subset of the plurality of simulated trips are run inparallel.
 28. The method of claim 27 wherein the subset of the pluralityof simulated trips are run on multiple cores either on the sameprocessor or different processors wherein one core manages a pluralityof agents running in the remaining cores, each agent simulating one ofthe plurality of electric vehicles traversing one of the plurality ofsimulated trips.
 29. The method of claim 1 further comprising: creatingfleet statistics specifying the performance of a fleet of electricvehicles comprising the plurality of simulated electric vehicles. 30.The method of claim 1 wherein the number of simulated trips is auser-supplied parameter.
 31. The method of claim 1 further comprising:determining that the state of charge of the battery has fallen below alow state of charge threshold; and tracking a number of times thecurrent node contains a vehicle that has fallen below the low state ofcharge threshold; and identifying as low state of charge hotspots thosenodes having the highest number of times the node contained a vehiclethat fell below the low state of charge threshold.